Need Help Troubleshooting

Hey everyone, I need your help once again!

We have a Micrologix 1400 PLC controlling and communicating to 3 Benshaw RSi S4 drives Via Modbus. Also included to that same Modbus network is a Hart HRT-710 for the flow meters.

There was a power outage at the customers site on Sunday. But after the mine electrician powered everything back up. The PLC wont communicate to the Drives anymore?, or very little.

However the flowmeter seem to be working fine? the customer notice an error light flashing on the Hart HRT-710 device.

We tried to recycle the power, but that did nothing!! except for the error light going away on the HRT-710

The PLC is using Message instructions' to communicate to the drive, but the Message instruction is also show errors?

I might need to drive up there tomorrow if I can't fix it remotely
P.S Everything was working fine prior to the power outage

Any ideas is very appreciated !!
Thanks everyone !!

richleva said:

The PLC is using Message instructions' to communicate to the drive, but the Message instruction is also show errors?

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Can you tell us specifically what error code(s) you're getting on each MSG instruction? That may be helpful. Also advise what, if any other hardware is present on your network.

I'm not familiar with Modbus, so hopefully someone else can help you dig deeper there.

The Message instruction says "Message time out in local processor".
There should be no other hardware attached to the Modbus network. Just the three drives and the Hart device HRT-710.

Thank you

Perhaps the drives that are no longer communicating reverted to their default port settings after the power outage and those settings aren't the same as what the PLC is using. Most people try to leave as many settings as possible at their default values to make replacement of components easier. In this case pay particular attention to the Modbus Device ID. Each device on a multidrop network must have a unique ID. The drives probably all default to the same ID, so that is a parameter that has to change on at least some of the drives.
The "Message timeout" tells you that a Modbus slave device, probably the drive failed to respond to a command from the Modbus master, presumably the PLC.

I got the customer to verify those configurations and they're all good?!
even parity and baudrate everything looks ok..

Thanks you

Modbus RTU is a daisy chain.


Going along with the same thinking as Steve, I would disconnect two of the three drives to see if it will start communicating. If it does the unit numbers need to be changed.

Regards,

richleva said:

The Message instruction says "Message time out in local processor".
There should be no other hardware attached to the Modbus network. Just the three drives and the Hart device HRT-710.

Thank you

Click to expand...

With AB, there is usually a Fault Code as well that might help you narrow the cause down. Can you ask your customer for any Error Codes? It isn't always obvious, so they will have to search for it.

Stu....

Hey Guys,

Went on site today, did the process of elimination and found that the second drive was defective. Called benshaw they say to pull the drive.

Thanks for the help everyone !!